Detection apparatus, detection method, and lithography apparatus

ABSTRACT

A detection apparatus includes an image pickup unit and a processor which detects a position of a mark using a two-dimensional image of the mark. The processor generates a one-dimensional signal having a plurality of peaks by accumulating images included in a detection region, detects peaks in which differences between values of the peaks and a reference value are equal to or larger than a threshold value and peaks in which differences between values of the peaks and the reference value are smaller than the threshold value from among the plurality of generated peaks and obtains a failure region in the mark, resets the detection region such that the differences between the values of the detected peaks and the reference value become smaller than the threshold value, generates a one-dimensional signal by accumulating images included in the reset detection region, and detects a position of the mark.

BACKGROUND OF THE INVENTION

Field of the Invention

One disclosed aspect of the embodiments relates to a detection apparatusand a detection method for detecting alignment marks formed on an objectand a lithography apparatus.

Description of the Related Art

In recent years, high accuracy and high functionality of semiconductorexposure apparatuses have been developed as miniaturization and highintegration of semiconductor circuit patterns of integrated circuits(ICs) and large-scale integrations (LSIs) are advanced. In particular,accuracy of alignment of an original, such as a mask or a reticle, and asubstrate, such as a semiconductor wafer or a glass plate, is importantsince the accuracy affects performance of apparatuses. Therefore, atechnique of aligning a pattern formed on an original and a shot regionset on a substrate with each other in nanometer order has been demanded.Accordingly, a position of the original is required to be exactlyobtained.

Alignment of an original relative to an original holding unit (a reticlestage) which holds the original is referred to as “reticle alignment”.In general, the alignment of the original relative to the reticle stageis performed by detecting a reticle mark formed on the original and areference mark formed on the reticle stage by a scope (a microscope).

Images of the reticle mark and the reference mark are captured by animage pickup element (such as a two-dimensional CCD sensor). The reticlemark and the reference mark enable measurement of positions thereofrelative to each other in an alignment direction (a measurementdirection). The images of the reticle mark and the reference markcaptured by the image pickup element are normally two-dimensionalimages. Accumulation is performed on each of the two-dimensional imagesof the reticle mark and the reference mark in a direction orthogonal tothe measurement direction (a non-measurement direction) so that aone-dimensional image signal (image data) is generated. As describedabove, to detect a mark, a method using one-dimensional image dataobtained by performing accumulation on a two-dimensional image in thenon-measurement direction may be employed (refer to Japanese PatentLaid-Open No. 2004-111861).

However, in a case where dust (foreign particles) adheres on the reticlemark or the reference mark or in a case where a defective portion isincluded in the reticle mark or the reference mark, when accumulation isperformed on each of the two-dimensional images of the marks in thenon-measurement direction, a one-dimensional image signal obtained bythe accumulation is changed (distorted) due to a factor not associatedwith the marks. Therefore, accuracy of detection of the marks may bedegraded, which affects accuracy of the alignment.

SUMMARY OF THE INVENTION

One disclosed aspect of the embodiments provides a detection apparatuswhich detects a mark including a plurality of mark elements. Thedetection apparatus includes an image pickup unit configured to capturean image of the mark, and a processor which detects a position of themark using a two-dimensional image of the mark obtained by the imagepickup unit. The processor generates a one-dimensional signal having aplurality of peaks by accumulating images included in a detection regionset in the two-dimensional image, detects peaks in which differencesbetween values of the peaks and a reference value are equal to or largerthan a threshold value and peaks in which differences between values ofthe peaks and the reference value are smaller than the threshold valuefrom among the plurality of peaks of the generated signal and obtains afailure region in the mark using results of the detection, and resettingthe detection region set in the two-dimensional image such that thedifferences between the values of the detected peaks and the referencevalue become smaller than the threshold value taking the obtainedfailure region into consideration and generating a one-dimensionalsignal having a plurality of peaks by accumulating images included inthe reset detection region, and detects a position of the mark inaccordance with the signal.

An aspect of the embodiments further provides a method for detecting aposition of a mark including a plurality of mark elements. The methodincludes capturing an image of the mark, generating a one-dimensionalsignal having a plurality of peaks by accumulating images included in adetection region set in the captured two-dimensional image of the mark,detecting peaks in which differences between values of the peaks and areference value are equal to or larger than a threshold value and peaksin which differences between values of the peaks and the reference valueare smaller than the threshold value from among the plurality of peaksof the generated signal, obtaining a failure region in the mark usingresults of the detection, resetting the detection region set in thetwo-dimensional image such that the differences between the values ofthe detected peaks and the reference value become smaller than thethreshold value taking the obtained failure region into consideration,generating a one-dimensional signal having a plurality of peaks byaccumulating images included in the reset detection region, anddetecting a position of the mark in accordance with the signal.

An aspect of the embodiments further provides a method for detecting aposition of a mark including a plurality of mark elements. The methodincludes capturing an image of the mark, obtaining a failure region ofthe mark, setting a detection region in the captured two-dimensionalimage of the mark such that the detection region does not include thefailure region, generating a one-dimensional signal having a pluralityof peaks by accumulating images included in the set detection region,and detecting a position of the mark in accordance with the signal.

An aspect of the embodiments further provides a detection methodincluding capturing an image of a mark including a plurality of markelements, setting a window in the mark image obtained by the capturing,generating a signal having a plurality of peaks by performingaccumulation on the mark image included in the window in a predetermineddirection, newly generating a signal having a plurality of peaks bynewly setting, in the mark image, a window having a width in thepredetermined direction which is reduced relative to the window, awindow which is located in a position different from a position of thewindow in the predetermined direction, or a window which has a width inthe predetermined direction reduced relative to the window and which islocated in a position different from a position of the window in thepredetermined direction, on the basis of differences between peaks ofthe plurality of peaks and performing accumulation on the mark image inthe newly-set window in the predetermined direction, and detecting aposition of the mark using the newly-generated signal having theplurality of peaks.

Further features of the disclosure will become apparent from thefollowing description of exemplary embodiments with reference to theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating a detection apparatus and a portion ofan exposure apparatus according to an embodiment.

FIG. 2 is a diagram illustrating a reticle mark and a reference mark.

FIG. 3 is a diagram illustrating a signal obtained by accumulatingimages of a mark included in a detection region.

FIG. 4 is a diagram illustrating a mark including a failure region andthe detection region.

FIG. 5 is a diagram illustrating a signal obtained by accumulatingimages of the mark including the failure region.

FIG. 6 is a flowchart illustrating a method for determining the failureregion.

FIG. 7 is a diagram illustrating a state in which the detection regionis set so as not to include the failure region.

FIG. 8 is a diagram illustrating a signal obtained by accumulatingimages of the mark which does not include the failure region.

FIG. 9 is a flowchart illustrating a method for determining the failureregion.

FIG. 10 is a graph illustrating threshold values used for adetermination of the failure region relative to the numbers of markelements in which light quantity peaks are changed.

FIG. 11 is a graph illustrating the relationship between an amount ofchange of a light quantity value and a measurement error of a markposition.

FIG. 12 is a flowchart illustrating a method for adjusting the detectionregion.

FIG. 13 is a diagram illustrating the method for adjusting the detectionregion.

FIG. 14 is a diagram illustrating another method for adjusting thedetection region.

FIG. 15 is a flowchart illustrating an exposure method using thedetection apparatus according to an embodiment.

DESCRIPTION OF THE EMBODIMENTS

An embodiment will be described in detail hereinafter with reference tothe accompanying drawings.

A detection apparatus MP will now be described. FIG. 1 is a diagramillustrating a state in which the detection apparatus MP of thisembodiment is applied to an exposure apparatus.

Method for Measuring Mark Positions

As a method for measuring positions of a mark, a method for detecting analignment mark formed on a reticle R or a reticle stage RS by thedetection apparatus MP and measuring a position of the alignment mark onthe basis of a result of the detection will be described. Furthermore, amethod for performing reticle alignment using a result of themeasurement of the position of the alignment mark of the reticle stageRS or the reticle R will be described.

The reticle R has a reticle mark RM formed thereon, and the detectionapparatus MP detects the reticle mark RM so as to obtain a position ofthe reticle R. The reticle R is conveyed to the reticle stage RS by areticle conveying mechanism, not illustrated. The reticle stage RS has areference mark SM formed thereon, and the detection apparatus MP detectsthe reference mark SM so as to obtain a position of the reticle stageRS.

A case where the reticle mark RM is formed on a lower surface of thereticle R (a surface of the reticle R which is in contact with thereticle stage RS) will be described in this embodiment. Furthermore, acase where the reference mark SM is formed on an upper surface of thereticle stage RS (a surface of the reticle stage RS which is in contactwith the reticle R) will be described.

As illustrated in FIG. 2, the reticle mark RM has an X mark RMX used tomeasure a position in an X direction and a Y mark RMY used to measure aposition in a Y direction which is orthogonal to the X direction, andthe reference mark SM has an X mark SMX used to measure a position inthe X direction and a Y mark SMY used to measure a position in the Ydirection. Here, each of the X marks and the Y marks has a plurality ofmark elements. For example, the Y mark of the reticle mark RM (the markRMY) includes mark elements RMB1 to RMB8. The Y mark includes markelements having a line shape extending in the X direction. By using themark elements of the line shape, a position of the mark may be obtainedby averaging results of detection of positions of the mark elements, andaccordingly, accuracy of position measurement of the mark may beenhanced.

The reticle R is conveyed to the reticle stage RS such that the reticlemark RM and the reference mark SM overlap with each other as illustratedin FIG. 2. The detection apparatus MP detects the reticle mark RM andthe reference mark SM so as to measure positions of the reticle R andthe reticle stage RS relative to each other.

The detection apparatus MP includes a reticle alignment scope RAS and animage processing unit P. The reticle alignment scope RAS includes alight source LS, an illumination optical system IL, an objective opticalsystem OL, and a camera CAM (image pickup unit) used to capture imagesof the reticle mark RM and the reference mark SM. The image processingunit P processes an image of the marks captured by the camera CAM so asto calculate positions of the reticle R and the reticle stage RSrelative to each other.

Specifically, the reticle alignment scope RAS captures a two-dimensionalmark image IMG including a reticle mark RM and a reference mark SM to bestored in an image storage unit P1 included in the image processing unitP. In the stored mark image IMG, a waveform generation unit P2 includedin the image processing unit P accumulates images in a region of ameasurement window WIN (a detection region) which is set to thetwo-dimensional image and which corresponds to regions in which themarks are formed in a direction orthogonal to a position measurementdirection. A one-dimensional signal (hereinafter referred to as an“accumulation waveform WA” is generated as illustrated in FIG. 3 byaccumulating the images (signals corresponding to light quantities) inthe direction orthogonal to the position measurement direction. Here,signals (light quantities) of the mark RMY included in a region of themeasurement window WIN illustrated in FIG. 2 are accumulated in the Xdirection, that is, a predetermined direction. In FIG. 3, an axis ofabscissa denotes a position in a non-accumulation direction (the Ydirection) of the measurement window WIN and an axis of ordinate denotesa result of accumulation of light quantities in an accumulationdirection (the X direction), that is, the predetermined direction, ofthe measurement window WIN. FIG. 3 is a graph illustrating relativelight quantities obtained when a maximum light quantity value is 100%.In this example, light quantities in the positions of the mark(positions of the mark elements) are small whereas light quantities inpositions in which the mark is not located (positions in which the markelements are not located) are large. It is recognized that nine lightquantity peaks are detected relative to the eight mark elements. In anormal state in which dust and a defect is not detected, light quantityvalues of the mark elements are substantially uniform.

A generated accumulation waveform WA is processed by a waveformprocessor P3 (a signal processor) included in the image processing unitP. The waveform processor P3 measures a position (in the Y direction) ofthe mark RMY of the reticle mark RM in the mark image IMG using theaccumulation waveform WA. As a method for measuring the position by thewaveform processor P3, a center of gravity of the accumulation waveformWA is calculated and processed so that the positions of the markelements included in the mark are calculated, the positions of the markelements are added to one another, and a resultant value is subjected toaveraging so that a center position of the mark is calculated.

Similarly, the measurement window WIN is set to the mark RMX of thereticle mark RM and images in the measurement window WIN in the capturedtwo-dimensional image are accumulated in the non-measurement direction(the Y direction) so that the one-dimensional accumulation waveform WAis generated. A position of the mark RMX of the reticle mark RM (in theX direction) in the mark image IMG is measured by processing thegenerated accumulation waveform WA. Furthermore, the same process isperformed by the image processing unit P on the marks SMX and SMY of thereference mark SM so as to measure a position (in the X direction) ofthe mark SMX of the reference mark SM and a position (in the Ydirection) of the mark SMY of the reference mark SM.

Results of the measurement of the positions of the reticle mark RM andthe reference mark SM performed by the image processing unit P aresupplied to a controller MC. According to the measurement results of thepositions of the marks, the positions of the reticle R and the reticlestage RS relative to each other and an amount of shift of the reticle Rrelative to the reticle stage RS are obtained. Therefore, when aprojection optical system PO of the exposure apparatus intends toproject a pattern of the reticle R on a substrate W, a position of thereticle stage RS is corrected so that alignment between the reticle Rand the substrate W may be performed at high accuracy. Alternatively, aposition of a substrate stage WS which moves a substrate chuck CH whichholds the substrate W is corrected so that alignment between the reticleR and the substrate W may be performed at high accuracy.

Case where Failure Region is Included

When a failure region DST caused by dust which adheres to one of themarks or caused by a defect of one of the marks is included in themeasurement window WIN as illustrated in FIG. 4, an accumulationwaveform WA illustrated in FIG. 5 is obtained and light quantity valuesof the mark elements are not uniform. A light quantity valuecorresponding to the measurement window WIN including the failure regionDST is small when compared with those of other regions, and a lightquantity difference LDF is generated relative to the maximum lightquantity value. If the position measurement described above is performedusing the accumulation waveform WA of FIG. 5, accuracy of themeasurement of the mark position may be lowered. Therefore, in anembodiment, the failure region DST is detected and the measurementwindow WIN is adjusted such that the region of the measurement windowWIN is not affected by the failure region DST. An image of a mark in theadjusted measurement window WIN is captured and a position of the markis measured using an accumulation signal obtained by performingaccumulation on the two-dimensional image, so that accuracy of themeasurement of the mark may be improved while an adverse effect of thefailure region DST is reduced.

Therefore, the image processing unit P of the detection apparatus MP ofthis embodiment includes a failure region determination unit P4 and awindow adjustment unit P5. After the mark image IMG captured by thereticle alignment scope RAS is stored in the image storage unit P1 ofthe image processing unit P, the failure region determination unit P4determines whether the failure region DST including dust or a defect isincluded in regions of the reticle mark RM and the reference mark SM.When the failure region determination unit P4 determines that thefailure region DST is included, the window adjustment unit P5 adjuststhe region of the measurement window WIN so that an adverse effect ofthe failure region DST is avoided. Thereafter, an image of the mark inthe measurement window WIN which is adjusted by the window adjustmentunit P5 is captured and the obtained two-dimensional image is subjectedto accumulation by the waveform generation unit P2 in a certaindirection so that an accumulation waveform WA is generated. Method forAdjusting Light Quantity Peaks of Accumulation Light Quantity

A method for measuring the positions of the reticle mark RM and thereference mark SM by the detection apparatus MP will be described withreference to a flowchart of FIG. 6, a mark image IMG of FIG. 7, and anaccumulation waveform of FIG. 8. First, the camera CAM captures a markimage IMG in a state in which the reticle mark RM and the reference markSM are included in an observation field of the reticle alignment scopeRAS (S101). The captured mark image IMG is transferred from the cameraCAM to the image processing unit P (S102). Next, the mark image IMG isprocessed so that it is determined whether the failure region DST isincluded in a mark in the region of the measurement window WIN (S103).As a result of the determination, when it is determined that the failureregion DST is included, the measurement window WIN is adjusted so as notto include the failure region DST (S104). Then an accumulation waveformWA is generated using the adjusted measurement window WIN, and aposition of the mark included in the measurement window WIN is measured(S105). As a result of the determination in step S103, when the failureregion DST is not included, an accumulation waveform WA is generatedusing the preset measurement window WIN and a position of the markincluded in the measurement window WIN is measured (S105). When thefailure region DST is included, the region of the measurement window WINis adjusted and reset such that the measurement window WIN does notinclude the failure region DST. When the accumulation waveform WA isgenerated using a two-dimensional image of the mark included in theadjusted and reset measurement window WIN, the accumulation waveform WAhas substantially uniform light quantity values (light quantity peaks)in the measurement window WIN as illustrated in FIG. 8. Since themeasurement window WIN is adjusted so as not to include the failureregion DST, differences among peak values of a plurality of peaksobtained from the accumulation waveform WA of the measurement window WINmay be reduced, and accordingly, the position of the mark may bemeasured while a measurement error is reduced. As described above, whenthe reticle mark RM and the reference mark SM are detected, thepositions of the reticle mark RM and the reference mark SM are measuredusing the accumulation waveforms WA generated by adjusting themeasurement window WIN.

Method for Determining Failure Region

The method for determining the failure region DST in step S103 describedabove will be described with reference to the mark image IMG of FIG. 4,the accumulation waveform WA of FIG. 5, and a flowchart of FIG. 9.First, among marks included in an image captured by the camera CAM ofthe reticle alignment scope RAS, a two-dimensional image of a markincluded in a range of the preset measurement window WIN are subjectedto accumulation so that an accumulation waveform WA is generated (S201).In the accumulation waveform WA, among values of a plurality of peakslocated in positions corresponding to spaces (gaps) between markelements, the largest peak value is set as a reference value LST (S202).In FIG. 5, a peak which appears between the mark element RMB1 and themark element RMB2 (a second light quantity peak from the left) has thelargest value.

Subsequently, values of the other peaks (accumulation light quantityvalues) of the accumulation waveform WA are compared with the referencevalue LST (a reference light quantity value) and determines whetherdifferences between the peak values and the reference value LST exceed athreshold value (S203). This determination is performed on the basis ofdifferences between the peaks of the accumulation waveform WA and thereference light quantity value. In FIG. 5, nine peaks are illustrated intotal, and the reference value LST is compared with values of the othereight light quantity peaks. Each of the peak values is compared with thereference value LST. Then at least one of the peaks in which adifference from the reference value LST does not exceed the thresholdvalue is categorized into a group A whereas at least one of the peaks inwhich a difference from the reference value LST exceeds the thresholdvalue is categorized into a group B (S204). Here, a peak having the samevalue as the reference value LST is categorized into the group A. Afterall the peaks included in the accumulation waveform WA are categorizedinto the group A or the group B, the number of peaks included in thegroup A and the number of peaks included in the group B are comparedwith each other (S205). As a result of the comparison, when the numberof peaks included in the group A is larger than that of the group B, itis determined that a failure region is included in a region includingthe peaks of the group B (S206). On the other hand, as a result of thecomparison, when the number of peaks included in the group B is largerthan that of the group A, it is determined that a failure region isincluded in a region including the peaks of the group A (S207). Here,although the failure region is detected provided that the number ofpeaks including the failure region is small, the failure region may bedetected provided that the number of peaks including the failure regionis large.

The threshold value may be appropriately determined in accordance with ameasurement error amount and accuracy obtained at a time when theposition of the mark is measured. A method for obtaining the thresholdvalue used for the determination of the failure region will be describedwith reference to FIGS. 1, 10, and 11. FIG. 10 is a diagram illustratingthreshold values for light quantities corresponding to the numbers ofpeaks in which values of the peaks are changed when the peaks obtainedfrom the accumulation waveform WA are compared with the reference valueLST. Different threshold values may be set for the different numbers ofpeaks in which values of the peaks are changed as represented by TH1 toTH8 of FIG. 10. As the number of peaks in which values of the peaks arechanged is small, a threshold value having a smaller ratio of a value ofa peak to the reference value (a threshold value corresponding to alarge change of a value of a peak relative to the reference value) isset. The different threshold values are set for different numbers ofpeaks in which the values of the peaks are changed since differentmeasurement error amounts may be obtained when a position of a mark ismeasured depending on a range of the failure region including dust on amark or a defect of a mark.

For example, in a case where the number of mark elements which areaffected by the failure region is small, the number of mark elementshaving small measurement error amounts is large, and accordingly, anerror amount of position measurement caused by the mark elements whichare affected by the failure region is small. Accordingly, as the numberof mark elements which are affected by the failure region is small, anacceptable amount of change of a value of a peak is large.

On the other hand, in a case where the number of mark elements which areaffected by the failure region is large, the number of mark elementshaving large measurement error amounts is large, and accordingly, anerror amount of position measurement caused by the mark elements whichare affected by the failure region is large. Accordingly, as the numberof mark elements which are affected by the failure region is large, anacceptable amount of change of a value of a peak is small.Alternatively, an arbitrary value may be set as the threshold value. Inthis case, although accuracy of the determination of the failure regionis degraded, the determinations of values of peaks may be comparativelyeasily performed.

As described above, the threshold value which is compared with thevalues of the plurality of peaks may be obtained by measuring therelationships between change amounts of the values of the peaks and anerror amount of the mark position measurement in advance. A case wherethe threshold value is obtained when a value of only one peak is changedwill be described with reference to FIG. 11. First, when a measurementerror amount of a mark position is obtained while a light quantity ofthe light source LS of the reticle alignment scope RAS is changed, alinear component LIN1 representing the relationship between an amount ofchange of the peak value and a measurement error of the mark position isobtained. Assuming that an acceptable mark position measurement errorobtained taking accuracy required for the position measurement deviceinto consideration is denoted by TH9, since the amount of the change ofthe peak value is represented by INT1 at this time, the threshold valueTH1 for the amount of the change of the peak value is determined asINT1[%].

Method for Adjusting Measurement Window

A method for adjusting the measurement window WIN will be described withreference to a flowchart of FIG. 12. The measurement window WIN isadjusted in a case where a failure region is included in a mark includedin the measurement window WIN, such as a case where foreign particlesadhere to the mark in the measurement window WIN or a case where adefect of the mark is detected. The region of the measurement window WINis not adjusted when the values of the plurality of peaks obtained fromthe accumulation waveform WA are not changed.

As the method for adjusting the measurement window WIN, first, a widthof the measurement window WIN is reduced by an arbitrary width in acertain direction (a first direction) along an accumulation directionwhich is a predetermined direction. Images (detection signals) obtainedby capturing the mark in the narrowed measurement window WIN areaccumulated so that an accumulation waveform WA is generated (S301).Thereafter, it is determined whether a difference between a value of apeak of the failure region and a value of a peak which is a referencevalue (a value of a peak of a region different from the failure region)is equal to or smaller than a threshold value (S302). When thedifference between the values of the peaks is not equal to or smallerthan the threshold value (that is, when the determination is negative),the process returns to step S301 where the measurement window WIN isfurther narrowed in the certain direction of the accumulation directionand an accumulation waveform WA of the measurement window WIN isobtained again. Then it is determined whether a difference between avalue of a peak of the narrowed detection region and the reference valueis equal to or smaller than the threshold value (S302). The measurementwindow WIN is repeatedly narrowed and an accumulation waveform WA isrepeatedly generated until the difference between a value of a peak of anarrowed detection region and the reference value becomes equal to orsmaller than the threshold value.

When the difference between the peak values becomes equal to or smallerthan the threshold value, a width of the measurement window WIN (a firstmeasurement window) in the accumulation direction and a centercoordinate of the measurement window WIN at this time are stored (S303).Subsequently, detection signals in the measurement window WIN areaccumulated in the accumulation direction so as to generate anaccumulation waveform WA. Contrast of the generated accumulationwaveform WA is obtained and it is determined whether the contrast isequal to or larger than a certain threshold value (S304). Since themeasurement window WIN is narrowed so as not to include the failureregion, values of peaks in the entire accumulation waveform WA arelowered, and therefore, the contrast is degraded. The degradation of thecontrast may cause degradation of accuracy of position measurement, andtherefore, the contrast of the accumulation waveform WA is checked. Thethreshold value for the contrast which does not degrade the accuracy ofthe position measurement may be obtained in advance. To suppress thedegradation of the accuracy of the position measurement, instead of thecontrast, a value of a peak of the detected accumulation waveform WA maybe used as a criterion for a determination.

When the contrast is equal to or larger than the threshold value, themeasurement window WIN at this time is determined as a detection region(S311). When the contrast is smaller than the threshold value, theregion before the measurement window WIN is narrowed in step S301 isobtained again, and the measurement window WIN is narrowed by anarbitrary width in a direction (a second direction) opposite to thedirection (the first direction) in which the measurement window WIN isnarrowed in step S301. An image (detection signals) obtained bycapturing the mark in the narrowed measurement window WIN are subjectedto accumulation so that an accumulation waveform WA is generated (S305).

It is determined whether a difference between a value of a peak in thefailure region and a value of a peak which is a reference value (a valueof a peak of a region different from the failure region) is equal to orsmaller than a threshold value (S306). When the difference between thevalues of the peaks is not equal to or smaller than the threshold value(that is, when the determination is negative), the process returns tostep S305 where the measurement window WIN is further narrowed in thedirection (the second direction) along the accumulation direction sothat an accumulation waveform WA in the measurement window WIN isobtained again. Then it is determined whether a difference between avalue of a peak of a further narrowed detection region and the referencevalue is equal to or smaller than the threshold value again from theaccumulation waveform WA of the mark in the detection region (S306). Themeasurement window WIN is repeatedly narrowed and an accumulationwaveform WA is repeatedly generated until the difference between a valueof a peak of a narrowed detection region and the reference value becomesequal to or smaller than the threshold value.

When the difference between the peak values becomes equal to or smallerthan the threshold value, a width in the accumulation direction of themeasurement window WIN (a second measurement window) and a centercoordinate of the measurement window WIN at this time are stored (S307).Subsequently, the image (the detection signals) obtained by capturingthe mark in the measurement window WIN is subjected to accumulation inthe accumulation direction so that an accumulation waveform WA isgenerated. Contrast of the generated accumulation waveform WA isobtained and it is determined whether the contrast is equal to or largerthan the certain threshold value (S308).

When the contrast is equal to or larger than the threshold value, themeasurement window WIN at this time is determined as a detection region(S311). When the contrast is smaller than the threshold value, theaccumulation waveform WA of the first measurement window WIN obtained instep S303 and the accumulation waveform WA of the second measurementwindow WIN obtained in step S307 are added to each other (S309). It isdetermined whether contrast of an accumulation waveform WA obtained byadding the accumulation waveforms WA of the two measurement windows WINto each other is equal to or larger than the threshold value (S310).When the contrast is equal to or larger than the threshold value, thefirst measurement window WIN obtained in step S303 and the secondmeasurement window WIN obtained in step S307 are determined as detectionregions for detection of a mark position (S311). When the contrast ofthe accumulation waveform WA obtained from the first measurement windowWIN and the second measurement window WIN is smaller than the thresholdvalue, the image processing unit P notifies the controller MC of a factthat measurement of a position of a mark after eliminating the failureregion may not be performed (S312).

Other Methods for Adjusting Measurement Window

As another method for adjusting the measurement window WIN, a methodwhich does not use mark elements in the failure region may be employed.When the mark illustrated in FIG. 2 is used, an accumulation waveform WAobtained by performing accumulation on an image obtained by capturingthe mark in the measurement window WIN has nine peaks since the markincludes the eight mark elements, and therefore, a position of the markis measured using values of the nine peaks. However, when the failureregion DST illustrated in FIG. 4 is included in the mark, theaccumulation waveform WA in the measurement window WIN illustrated inFIG. 5 is obtained. Therefore, the position of the mark may be measuredusing values of peaks which are equal to or larger than the thresholdvalue without using light quantity peaks smaller than the thresholdvalue (an accumulation waveform WA in the failure region). Themeasurement of the position of the mark is performed without usingvalues of third to fifth peaks from the left among the nine peaks butusing values of the other six peaks among the values of the nine peaks.In this case, although accuracy of measurement of the position of themark is degraded since the number of peaks (the number of mark elements)used for the measurement is reduced, the measurement window WIN may beadjusted by a comparatively simple process.

Furthermore, as another method for adjusting the measurement window WIN,different settings of the measurement window WIN are applied to markelements including the failure region DST and mark elements which do notinclude the failure region DST as illustrated in FIG. 13. For example,in a region including the mark elements RMB2, RMB3, and RMB4 whichinclude the failure region DST, a measurement window WIN2 having a widthadjusted by the adjustment method described above is used as a detectionregion. On the other hand, in a region including the mark element RMB1and a region including the mark elements RMB5 to RMB8, measurementwindows WIN3 having predetermined widths may be used as detectionregions. Since the different measurement windows are used for the markelements including the failure region DST and the mark elements which donot include the failure region DST, an accumulation waveform WA havinghigher contrast may be obtained in the region other than the failureregion when the accumulation waveform WA is generated and measurementaccuracy may be enhanced.

In the embodiment described above, an image of marks is captured by thecamera CAM and an accumulation waveform WA to be processed is generatedby performing accumulation on the captured two-dimensional image in theaccumulation direction. However, the camera CAM or a sensor whichcaptures the image of the marks is not limited to a camera using atwo-dimensional CCD sensor. For example, a one-dimensional accumulationwaveform may be obtained while scanning is performed in the accumulationdirection by a light quantity sensor on a mark. A range of the scanningcorresponds to the measurement window WIN of this embodiment.

As described above, according to the detection method of thisembodiment, even when a failure region is included in a mark to bemeasured, accuracy of detection of the mark is improved by detecting thefailure region and adjusting the measurement window WIN. It is expectedthat, using a result of the detection, a measurement error of a positionof a mark is reduced and the position measurement is performed at higheraccuracy.

Furthermore, as the method for adjusting the measurement window WIN,images of a mark obtained by capturing the mark included in themeasurement window WIN may be accumulated in a direction orthogonal tothe accumulation direction described above so that the failure region isspecified. In a case of the failure region including dust, for example,when the images of the mark are accumulated in the direction orthogonalto the accumulation direction, a light quantity of the failure region isreduced. Accordingly, the failure region may be specified.

Furthermore, as the method for adjusting the measurement window WIN, thefailure region may be specified by template matching as illustrated inFIG. 14. The measurement window WIN is adjusted such that the failureregion specified by the template matching is not included in themeasurement window WIN. A degree of correlation between a mark to bemeasured and a template TP is obtained by the template matching. Sinceit is likely that the degree of correlation is lowered in the failureregion DST, the measurement window WIN is determined by excepting aregion having a low degree of correlation.

Exposure Apparatus

An exposure apparatus including the detection apparatus according to anembodiment will be described. An exposure method employed in theexposure apparatus in which the projection optical system PO projects apattern of the reticle R on the substrate W will be described withreference to a flowchart of FIG. 15.

The reticle R is conveyed to the reticle stage RS by the reticleconveying mechanism, not illustrated (S401). Subsequently, a positionshift amount of the reticle R relative to the reticle stage RS ismeasured (S402). The relative position shift amount is measured bydetecting the reticle marks RM and the reference marks SM by thedetection method described above and performing image processing onresults of the detection by the image processing unit P so as to measurepositions of the reticle marks RM and the reference marks SM relative toeach other. The position shift amount is obtained from the positions ofthe reticle marks RM and the reference marks SM relative to each other,and the reticle stage RS is driven so that the reticle R is aligned(S403).

After the alignment of the reticle R, the substrate W is conveyed on thesubstrate chuck CH disposed on the substrate stage WS by a substrateconveying mechanism, not illustrated (S404). When the substrate W isconveyed on the substrate chuck CH, alignment marks are detected using ascope (a substrate alignment scope), not illustrated, so that thesubstrate stage WS is aligned. The conveyance of the reticle R and theconveyance of the substrate W may be performed in parallel. After thesubstrate W is disposed on the substrate stage WS, the pattern of thereticle R is exposed on the substrate W (S405). The exposure process(pattern transfer) may be performed on an entire surface of thesubstrate W by repeatedly exposing the pattern of the reticle R on thesubstrate W (S406). After the pattern transfer performed on the entiresurface of the substrate W is completed, the substrate W is carried outby the substrate conveying mechanism (S407). When a substrate to beprocessed exists, the process from step S404 to step S407 is performedagain, whereas when a substrate to be processed does not exist, theprocess is terminated after the reticle R is carried out (S408 andS409). Note that the carrying-out of the reticle R and the carrying-outof the substrate W may be performed in parallel.

As the exposure apparatus described above, a stepper which successivelytransfers a pattern formed on an original (a reticle, for example) in aplurality of portions in a substrate (a wafer, for example) while movingthe substrate in a stepping manner may be used. Alternatively, a scannerwhich transfers a pattern on a substrate while driving a substrate stagewhich holds a substrate and a reticle stage which holds a reticlerelative to each other may be used as the exposure apparatus. Thedetection apparatus described above may be employed in not only theexposure apparatus but also other lithography apparatuses, such as animprint apparatus. The imprint apparatus may form a pattern on animprint member supplied on a substrate using a mold serving as anoriginal. The reference marks SM may be formed on a mold holding unitwhich holds the mold and marks (mold marks) corresponding to the reticlemarks RM described above may be formed on the mold so that a position ofthe mold relative to the mold holding unit is measured.

The case where the detection apparatus is applied to the exposureapparatus or the imprint apparatus has been described hereinabove. Sincethe reticle stage RS and the substrate stage WS are driven in accordancewith positions of the reticle (the original) and the reticle stage (theoriginal holding unit) which are relative to each other so that thealignment is performed, the reticle may be aligned relative to the wafer(the substrate) at high accuracy.

Although the preferred embodiment has been described hereinabove, thedisclosure is not limited to the embodiment described above, and variousmodifications and alternations may be made within the scope of thedisclosure.

While the disclosure has been described with reference to exemplaryembodiments, it is to be understood that the disclosure is not limitedto the disclosed exemplary embodiments. The scope of the followingclaims is to be accorded the broadest interpretation so as to encompassall such modifications and equivalent structures and functions.

This application claims the benefit of Japanese Patent Application No.2014-008064, filed Jan. 20, 2014, which is hereby incorporated byreference herein in its entirety.

What is claimed is:
 1. A detection apparatus which detects a position ofa mark including a plurality of mark elements, the detection apparatuscomprising: an image pickup unit configured to capture a two-dimensionalimage of the mark; and a processor which detects a position of the markusing the two-dimensional image of the mark obtained by the image pickupunit, wherein the processor sets a detection region in thetwo-dimensional image of the mark, generates a one-dimensionalintegrated signal having a plurality of peaks by accumulating, in apredetermined direction, a two-dimensional image signal included in thedetection, detects peaks in which differences between values of thepeaks and a reference value are equal to or larger than a thresholdvalue and peaks in which differences between values of the peaks and thereference value are smaller than the threshold value from among theplurality of peaks of the generated integrated signal in order todetermine if a failure region is present within the detection region,and in a case where a failure region is present within the detectionregion, the processor narrows a width of the detection region in thepredetermined direction until the failure region is excluded so as toform a new detection region that does not include the failure region,generates a new one-dimensional integrated signal having a plurality ofpeaks by accumulating, in the predetermined direction, a two-dimensionalimage signal included in the new detection region, and detects aposition of the mark based on the new one-dimensional integrated signal.2. The detection apparatus according to claim 1, wherein the markincludes a plurality of lines each of which is parallel with each otherserving as the mark elements, and the processor accumulates imagesincluded in the detection regions along the lines.
 3. The detectionapparatus according to claim 1, wherein the processor sets a largestvalue of a peak among the plurality of peaks as a reference value andcompares the values of the plurality of peaks with the reference valueso as to obtain differences between the values of the plurality of peaksand the reference value.
 4. The detection apparatus according to claim1, wherein the processor determines, when the number of peaks in whichdifferences between values of the peaks and the reference value areequal to or larger than the threshold value is smaller than the numberof peaks in which differences between values of the peaks and thereference values are smaller than the threshold value, that a failureregion of the mark is included in positions of the peaks in which thedifferences between the values of the peaks and the reference value areequal to or larger than the threshold value, and resets the detectionregion to the two-dimensional image taking the failure region intoconsideration.
 5. The detection apparatus according to claim 1, whereinthe processor determines, when the number of peaks in which differencesbetween values of the peaks and the reference value are equal to orlarger than the threshold value is larger than the number of peaks inwhich differences between values of the peaks and the reference valuesare smaller than the threshold value, that a failure region of the markis included in positions of the peaks in which the differences betweenthe values of the peaks and the reference value are smaller than thethreshold value, and resets the detection region to the two-dimensionalimage taking the failure region into consideration.
 6. The detectionapparatus according to claim 1, wherein the threshold value is obtainedon the basis of the number of peaks in which differences between valuesof the peaks and the reference value are generated.
 7. The detectionapparatus according to claim 1, wherein the new detection regioncomprises at least a firs window and a second window, wherein eachwindow has mark elements and excludes the failure region, and whereinthe first window has a width that is narrower than a width of the secondwindow with respect to the predetermined direction.
 8. The detectionapparatus according to claim 1, wherein the detection region comprises aplurality of windows including the plurality of the mark elements,wherein the widths of the windows are narrowed with respect to thepredetermined direction such that the failure region is removed from thewindows.
 9. A method for detecting a position of a mark including aplurality of mark elements, the method comprising: capturing atwo-dimensional image of the mark; setting a detection region in thetwo-dimensional image of the mark; generating a one-dimensional signalhaving a plurality of peaks by accumulating, in a predetermineddirection, a two-dimensional image signal included in a detectionregion; detecting peaks in which differences between values of the peaksand a reference value are equal to or larger than a threshold value andpeaks in which differences between values of the peaks and the referencevalue are smaller than the threshold value from among the plurality ofpeaks of the generated signal in order to determine if a failure regionis present within the detection region; in a case where a failure regionis present within the detection region, narrowing the width of thedetection region in the predetermined direction until the failure regionis excluded so as to form a new detection region that does not includethe failure region, and generating a new one-dimensional integratedsignal having a plurality of peaks by accumulating, in the predetermineddirection, a two-dimensional image signal included in the new detectionregion; and detecting a position of the mark based on the newone-dimensional integrated signal.
 10. A lithography apparatus whichforms a pattern on a substrate using an original, the lithographyapparatus comprising: an original holding unit configured to hold theoriginal; and a detection apparatus configured to detect a markincluding a plurality of mark elements which are formed on the originaland the original holding unit, wherein the detection apparatus includesan image pickup unit configured to capture a two-dimensional image ofthe mark, and a processor which detects a position of the mark using thetwo-dimensional image of the mark obtained by the image pickup unit, andthe processor sets a detection region in the two-dimensional image ofthe mark, generates a one-dimensional signal having a plurality of peaksby accumulating images included in the detection region, detects peaksin which differences between values of the peaks and a reference valueare equal to or larger than a threshold value and peaks in whichdifferences between values of the peaks and the reference value aresmaller than the threshold value from among the plurality of peaks ofthe generated signal in order to determine if a failure region ispresent within the detection region, and in a case where a failureregion is present within the detection region, the processor narrows thewidth of the detection region in the predetermined direction until thefailure region is excluded so as to form a new detection region thatdoes not include the failure region, generates a new one-dimensionalintegrated signal having a plurality of peaks by accumulating, in thepredetermined direction, a two-dimensional image signal included in thenew detection region, and detects a position of the mark based on thenew one-dimensional integrated signal.